DESCRIPTION: The freezing characteristics of spheroids are unique and differ from that of the isolated cells which comprise the aggregate. The characterization of the low temperature properties will be essential to the development of cryopreservation protocols for spheroids. Two different experimental systems of interest will be investigated: spheroids made from hepatocytes and prostate tumor cells. These two systems were chosen because of their clinical relevance. Hepatocyte spheroids are presently under investigation for use in a Bio-Artificial Liver. Prostate spheroids have been used previously to test the effectiveness of different treatment modalities on prostate cancer. The specific aims of this investigation are: (1) to determine the basic cryobiophysical parameters of isolated cells which form the aggregates; (2) to determine the basic cryobiophysical parameters for the spheroids during freezing; (3) to develop single as well as multicompartment models for the water transport within a spheroid; (4) to freeze spheroids using a controlled rate freezer under different thermal and chemical conditions and determine the spatial distribution of viable cells within the spheroid and functional viability; (5) to develop methods of enhancing viability for hepatocyte spheroids and damage for tumor spheroids during cryopreservation. The results of this investigation will provide a rational basis for the development of freezing protocols for cryopreservation as well as cryosurgical protocols. Successful cryopreservation of hepatocyte spheroids will facilitate the clinical applications of spheroid-based liver support systems. Determination of the damage mechanisms and methods to enhance damage will facilitate development of cryosurgical protocols for the treatment of prostate cancer.